JP2003087508A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a conventional semiconductor laser driving circuit in which a droop characteristic of a semiconductor laser is corrected is too expensive because of an exclusive circuit. SOLUTION: A droop characteristic is corrected by controlling a bias current of a semiconductor laser, a control part composed of a switching element, etc., is connected to a general purpose semiconductor laser drive IC, and the switching element is corrected with a control signal for droop correction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to drive control of a semiconductor laser as an image writing means.

[0002]

2. Description of the Related Art A drive control of a semiconductor laser as an image writing means is performed by an APC (Auto Power Control).
roll) is used. The APC is a control for keeping the output of the semiconductor laser constant by detecting the output light of the semiconductor laser with a photosensor and feeding back the detected value to the drive current of the semiconductor laser.

[0003]

In APC, feedback control is performed for each scanning line, but the semiconductor laser has a droop characteristic that the amount of light decreases due to heat generated by light emission. Therefore, even if the light emission unevenness between the lines is corrected by the APC, there is a problem that the light emission amount differs between the head and the tail of one line. In particular, when an image is formed by continuously turning on the semiconductor laser, the density variation due to the droop characteristic becomes remarkable. In the image forming process in which toner is attached to the exposed portion to form an image, the phenomenon that the density of the tail of one line becomes lower than the density of the leading portion occurs, and in the image formation in which the toner is attached to the unexposed portion, There is a problem that the background density becomes high at the tail of one line.

As a measure against the problem caused by the droop characteristic, in Japanese Patent Laid-Open No. 10-135558, the on / off time ratio of the image data for each scanning line is obtained prior to the image formation, and the obtained time ratio is obtained. A drive control method for controlling the bias current of a semiconductor laser is proposed based on the above-mentioned Japanese Patent Application Laid-Open No. 11-291547, and a light quantity difference in one scanning line is obtained for each pixel, and each pixel is calculated based on the obtained light quantity difference information. A drive control method for controlling the above has been proposed.

However, each of the above-mentioned conventional drive control methods requires a dedicated drive circuit, which raises the problem that the cost of the semiconductor laser drive means increases.
On the other hand, in recent years, high-performance and inexpensive semiconductor laser drive ICs are commercially available.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus in which unevenness in light amount due to droop characteristics is satisfactorily corrected by using a commercially available semiconductor laser driving IC.

[0007]

The above-mentioned objects of the present invention are achieved by the following inventions.

1. A semiconductor laser, a laser drive circuit for driving the semiconductor laser, a drive means for supplying a drive current based on image data to the laser drive circuit, a continuous lighting detection means for detecting a continuous lighting state in one line based on the image data, An image forming apparatus comprising: a switching element for controlling a bias current of the semiconductor laser; and a control pulse generating means for generating a pulse for controlling the switching element based on an output of the continuous lighting detecting means.

2. 2. The image forming apparatus as described in 1 above, further comprising a line memory for synchronizing the driving unit and the control pulse generating unit.

3. There is a control means for generating a control signal for controlling the control pulse generation means based on the output of the continuous lighting detection means, and the control means stores the first correction data corresponding to the droop characteristic of the semiconductor laser. 3. The image forming apparatus as described in 1 or 2 above.

4. The LUT stores second correction data for performing shading correction of the exposure optical system, and the control means calculates the first correction data and the second correction data to generate the control signal. The image forming apparatus described in 3 above.

5. 4. The image forming apparatus as described in 3 above, wherein the first correction data is for correcting the bias current in a decreasing direction.

6. A semiconductor laser, a laser drive circuit for driving the semiconductor laser, a drive means for supplying a drive current based on image data to the laser drive circuit, a continuous lighting detection means for detecting a continuous lighting state in one line based on the image data, Control means for generating a control signal based on the output of the continuous lighting detection means, a D / A converter for converting the control signal from the control means, and a semiconductor laser of the semiconductor laser based on the output of the D / A converter. An image forming apparatus having a voltage / current conversion circuit for controlling a bias current.

7. 7. The image forming apparatus as described in 6 above, further comprising a line memory for synchronizing the driving unit and the control unit.

8. 8. The image forming apparatus according to 6 or 7, wherein the control unit has an LUT storing first correction data according to the droop characteristic of the semiconductor laser.

9. The LUT stores second correction data for performing shading correction of the exposure optical system, and the control means calculates the first correction data and the second correction data to generate the control signal. 9. The image forming apparatus described in 8 above. 10. 9. The image forming apparatus as described in 8 above, wherein the first correction data is for performing correction in a direction of decreasing the bias current.

[0017]

1 shows an image forming apparatus according to an embodiment of the present invention.

The originals placed on the original conveying apparatus 1 are conveyed one by one and then to the reading position. At the reading position, the original is illuminated by the lamp 3 of the reading unit 2, and the reflected light is incident on the image sensor 9 through the mirrors 5, 6, 7 and the lens 8 of the reading unit 2.

Further, the document placed on the platen glass 4 is read by the movement of the scanning unit composed of the lamp 3 and the mirror 5.

Based on the image data generated by reading the original, the photoconductor 11 is scanned and exposed by the exposure device 10 having a semiconductor laser as a writing means, and the latent image formed on the photoconductor 11 by the exposure is It is developed by the developing device 12. The toner image on the photoconductor 11 is transferred by the transfer device 16 to the recording paper fed from the paper supply unit 13, 14 or 15, and the transferred toner image is fixed on the recording paper by the fixing device 17. The toner image on which the toner image is fixed is discharged to the paper discharge unit 18.

FIG. 2 shows the structure of the exposure apparatus 10. The laser light L emitted from the semiconductor laser 20 is shaped by the collimator lens 21 and enters the rotary polygon mirror 23 via the first cylindrical lens 22. The laser light L is deflected by the rotary polygon mirror 23 in the range of L1 and L2, and enters the photoconductor 11 via the fθ lens 24 and the second cylindrical lens 25.

FIG. 3 shows a laser drive control circuit of the image forming apparatus according to the first embodiment of the present invention.

Laser diode LD and photo sensor PD
The semiconductor laser 20 consisting of is driven by a laser driving IC 33 as a laser driving circuit and emits light. The laser driving IC is, for example, S manufactured by Texas Instruments
N65ALS541 / A and Mitsubishi Electric M6188OFP
Etc. are used. The laser drive IC 33 supplies the semiconductor laser 20 with the drive current ID and the bias current IB. The drive current ID is a pulse current generated by pulse input in which the image data DATA is pulse-width modulated by the modulator 34 as a driving unit. The image data delayed by one line is supplied from the line memory 37 to the modulator 34.
And the modulator 34 are synchronized with each other.

The semiconductor laser 20 emits laser light by a current obtained by adding the drive current ID and the bias current IB.
The control of the bias current IB will be described below.

The bias current IB is controlled on the basis of the current obtained by converting the control pulse generated by the modulator 31 as the control pulse generating means by the transistor 32 as the switching element. Reference numeral 35 denotes a continuous lighting detecting means, which is a semiconductor laser 2 for one line from image data for one line.
The continuous lighting length of 0 is detected. That is, for example, the continuous portion of the image data indicated by L1 and L2 in FIG. 4 is detected.

In the image formation by reversal development, an image in which the highest density portion is continuous is formed by continuously lighting the semiconductor laser 20. Also, in image formation by regular development,
The background portion is formed by continuous lighting of the semiconductor laser 20. The continuous lighting detecting means 35 detects the continuous length of the maximum density value or the continuous length of the background density value from the image data DATA to continuously light the semiconductor laser 20.
1, L2 is detected. Reference numeral 30 denotes a control unit that controls the modulation unit 31 with reference to the LUT 36 based on the output of the continuous lighting detection unit 35.

FIG. 4 shows the emission characteristics of the semiconductor laser 20 during continuous lighting. In the figure, DATA is image data, and LDout is the emission intensity of the semiconductor laser 20.
When the semiconductor laser is continuously lit as shown by the dotted line in the figure, the semiconductor laser 20 has a droop characteristic in which the emission intensity thereof is attenuated corresponding to the continuous time. The correction in the present invention corrects the light emission characteristic indicated by the dotted line f1 to the light emission characteristic indicated by the solid line f2 by the correction in the direction of decreasing the bias current. In the LUT 36, the droop characteristic is measured in advance and the corresponding first correction data is stored.
The first correction data cs2 is used to correct the output LDout of the semiconductor laser 20 shown by the dotted line f1 in FIG. 4 to the output shown by the solid line f2.

FIG. 5 shows the correction for the shading characteristics of the exposure optical system. When the shading correction is not performed, as shown by the dotted line f1, due to the shading characteristics of the optical system of the exposure device, the exposure intensity is high at the center of the image and low at both ends. By correcting the output of the semiconductor laser 20 by shading correction, the exposure intensity is corrected from the dotted line f1 to the solid line f2. The second correction data cs3 for shading correction is also stored in the LUT 36 by measuring the characteristics of the exposure apparatus in advance. Second
The correction data cs3 is obtained, for example, by measuring the surface potential of the photoconductor 11 after exposure by the potential sensor 38 in FIG. Further, the second correction data cs3 obtained by measuring the toner image density on the photoconductor 11 after development can also be used.

The continuous lighting detection means 35 measures the continuous length of the image data and inputs the continuous length information cs1 to the control means 30. The control means 30 uses the continuous length information cs1 and the LUT.
The pulse width modulation of the modulator 31 is controlled by calculating the correction amount from the first correction data cs2 and the second correction data cs3 read out from 36.

FIG. 6 shows bias current correction by pulse width modulation. (A) shows the level of correction, which is the maximum correction value CPmax, the intermediate correction value CPmed, and the uncorrected CPmi.
It is represented by n. (B) is an image clock, and FIG.
Is input to the modulator 31. 2C shows the output of the modulator 31 in FIG. 2, in other words, the output of the transistor 32. The terminal RS of the laser driving IC 33 is held at a constant voltage. When the bias current when the transistor 32 is off is IB0, the bias current IB when the transistor 32 is on and the current IG flows is IB0-IG, as shown in FIG. 6D. The average value of the bias current IB is IB0-IG at CPmax, IB0 at CPmin, and intermediate at CPmed.

With the correction described above, the semiconductor laser 2
As a result of the correction of the droop characteristic of 0 and the shading correction, the semiconductor laser 20 emits light accurately corresponding to the image data, and an image having a uniform image density characteristic is obtained.

FIG. 7 shows a laser drive control circuit of the image forming apparatus according to the second embodiment of the present invention.

The same parts as those in FIG. 1 are designated by the same reference numerals. The digital output of the control means 30 is the D / A converter 40.
Is converted to an analog value by the voltage / current conversion circuit 41 including operational amplifiers U1, U2 and R1 to R4. The resistor RG is for making the current IG.

The LUT 36 stores first correction data for droop characteristic correction and second correction data for shading correction. The bias current IB has a correction amount calculated by the control unit 30 based on the continuous length information cs1 of the continuous lighting detection unit, the first correction data cs2 for correcting the droop characteristic of the semiconductor laser, and the second correction data cs3 for performing the shading correction. It corresponds to the output of the D / A converter 40 based on the above. As the D / A converter 40,
For example, if an 8-bit type is used, it becomes possible to control the laser driving IC 33 with a resolution of 256 steps.

[0035]

According to the invention of claim 1, 2, 3 or 5,
By connecting a circuit such as a switching element to a general-purpose laser driving IC, the droop characteristic of the semiconductor laser is corrected well, so that an image forming apparatus that forms a high-quality image with uniform image density characteristics is low. Realized at cost.

According to the invention of claim 4 or 9, it is possible to form a high-quality image having uniform image density characteristics with shading correction.

According to the invention of claim 6, 7, 8 or 10,
By connecting a D / A converter or the like to a general-purpose laser drive IC, the droop characteristic of the semiconductor laser is corrected well, so that an image forming apparatus that forms a high-quality image with uniform image density characteristics is provided. It is realized at low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an exposure apparatus.

FIG. 3 is a diagram showing a laser drive control circuit of the image forming apparatus according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a light emission characteristic when a semiconductor laser is continuously turned on.

FIG. 5 is a graph showing correction for shading characteristics of an exposure optical system.

FIG. 6 is a diagram showing correction of a bias current by pulse width modulation.

FIG. 7 is a diagram showing a laser drive control circuit of an image forming apparatus according to a second embodiment of the present invention.

[Explanation of symbols] 20 Semiconductor laser 30 control means 31, 34 Modulator 32 transistors 33 Laser drive IC 35 Continuous lighting detection means 36 LUT 37 line memory 40 D / A converter 41 Voltage / current conversion circuit

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Claims (10)

[Claims] 1. A semiconductor laser, a laser drive circuit for driving the semiconductor laser, a driving means for supplying a drive current based on image data to the laser drive circuit, and a continuous lighting state in one line is detected based on the image data. Continuous lighting detection means, a switching element for controlling the bias current of the semiconductor laser, and a control pulse generation means for generating a pulse for controlling the switching element based on the output of the continuous lighting detection means apparatus. 2. The image forming apparatus according to claim 1, further comprising a line memory for synchronizing the driving unit and the control pulse generating unit. 3. A control means for generating a control signal for controlling the control pulse generation means based on an output of the continuous lighting detection means, the control means having a first correction according to a droop characteristic of the semiconductor laser. The image forming apparatus according to claim 1 or 2, further comprising an LUT storing data. 4. The LUT stores second correction data for performing shading correction of an exposure optical system, and the control means calculates the first correction data and the second correction data to generate the control signal. The image forming apparatus according to claim 3, wherein: 5. The image forming apparatus according to claim 3, wherein the first correction data is for correcting the bias current in a decreasing direction. 6. A semiconductor laser, a laser drive circuit for driving the semiconductor laser, driving means for supplying a drive current based on image data to the laser drive circuit, and a continuous lighting state in one line is detected based on the image data. Continuous lighting detection means, control means for generating a control signal based on the output of the continuous lighting detection means, D / A converter for converting the control signal from the control means, based on the output of the D / A converter An image forming apparatus comprising a voltage / current conversion circuit for controlling a bias current of the semiconductor laser. 7. The image forming apparatus according to claim 6, further comprising a line memory for synchronizing the drive unit and the control unit. 8. The image forming apparatus according to claim 6, wherein the control unit has an LUT that stores first correction data according to the droop characteristic of the semiconductor laser. 9. The LUT stores second correction data for performing shading correction of an exposure optical system, and the control means calculates the first correction data and the second correction data to generate the control signal. The image forming apparatus according to claim 8, wherein. 10. The image forming apparatus according to claim 8, wherein the first correction data is for correcting the bias current in a decreasing direction.